It is well known in agriculture that the location in the soil of seed relative to fertilizer is an important factor in maintaining healthy plants. With many crops it is often beneficial to have a relatively small amount of most types of fertilizer very near the seed, however excessive amounts of fertilizer are known to damage seedlings. Safe fertilizer application rates depend on the proximity of the seed to the fertilizer. If the seed and fertilizer are spread over a wide band, the safe rate is much higher than if the seed and fertilizer are placed together and concentrated in a narrow band.
The simplest seeding implements deposit seed from one tank and fertilizer from another into a single delivery tube that carries the mixture of seed and fertilizer from the tanks to the furrow openers and deposits it in a single furrow made by a furrow opener. Where the mixture is spread over a wide band using a wide furrow opener, quite high rates of some fertilizers may be safely applied however, in the minimum tillage agriculture common today, it is generally desirable to disturb the soil as little as possible, and so narrow openers on wider row spacings are popular. The wider row spacing requires that, in order to achieve a desired application rate of pounds of fertilizer and seed per acre, more product must be placed in each row. These narrow openers spaced farther apart concentrate the seed and fertilizer in a narrow band, greatly limiting the amount of fertilizer that can be mixed with the seed.
The amount of fertilizer that can safely be deposited with the seed varies dramatically depending on the type of fertilizer. Some fertilizers, notably nitrogen in its various forms, cause significant seedling damage at application rates much lower than those typically desired to maximize yield. For this reason nitrogen has historically been deposited in or on the soil in a separate operation prior to seeding, or sometimes after seeding. Granular nitrogen fertilizer is available in an ammonium nitrate form and a urea form, and for many crops the safe application rate of the ammonium nitrate form is somewhat higher than for the urea form. Liquid nitrogen often contains both ammonium nitrate and urea. Nitrogen moves readily through the soil and so can be placed a considerable distance from the seed and still be effective.
Sulfur fertilizer is commonly provided in the form of ammonium-sulphate, and contains a significant proportion of nitrogen in addition to the desired sulfur. Ammonium-sulphate can also damage seedlings when applied at commonly desired rates. Safe rates of application are generally determined by adding the nitrogen content of the ammonium-sulphate to the amount of nitrogen being applied. Similar to nitrogen, sulfur also moves readily through the soil and so can be placed a considerable distance from the seed.
Fertilizers to provide phosphate are also commonly applied, typically at substantially lower rates than nitrogen. These are generally less damaging to seedlings than nitrogen and safe application rates of these fertilizers for most crops is thus higher. Phosphorus fertilizers are also typically applied at lower rates than nitrogen. Phosphate does not move readily in the soil and thus, for satisfactory results, should not be placed too far away from the seed.
Potassium fertilizers are also commonly used typically in the form of potassium chloride. While potassium fertilizer moves more readily through the soil than phosphorus, it is generally accepted that proximity of the chloride to the seedlings is beneficial, perhaps because of an anti-bacterial effect, and so it is desirable to place a portion of the potassium fertilizer with or at least near the seed.
Cereal crops are much less susceptible to seedling damage from fertilizer than are canola and flax crops. Canola and flax are very susceptible to damage from nitrogen especially. Canola generally requires sulfur fertilizer as well, which also contains a significant proportion of nitrogen and so can also cause damage.
Thus the consideration of the optimum placement of fertilizer relative to seed requires consideration of a fairly complex set of factors. In addition, safe application rates also vary significantly with soil type, soil temperature, and soil moisture. Fertilizers may be blended together for placement, and are available in both liquid and granular forms.
Air seeders have become a common implement for seeding and have been adapted to both seed and provide fertilizer in a single pass. Air seeders typically comprise a cart carrying two, three, or more holding tanks for holding particulate agricultural products such as seed and fertilizer. Liquid fertilizer is also often carried in a tank on the same cart or on a separate cart. The agricultural products are delivered through delivery tubes to one or more sets of furrow openers in separate or combined streams. Other types of seeders could also be used to provide the furrows and deposit the appropriate agricultural products in the furrows.
Seeders have taken two distinct routes in their methods of providing both seed and fertilizer in a single pass. In the first, double shoot and triple shoot side banding machines deliver two or three separate streams of agricultural products to a furrow opener assembly. Typically one of the streams will contain all the seed and possibly a small amount of fertilizer, typically phosphate, and the other streams will contain the balance of the fertilizer which may be either a single fertilizer or a blend of the desired fertilizer. The furrow opener assembly is configured to place the streams into closely adjacent bands in the soil, generally about one to two inches apart. In some machines the seed stream will be divided into two separate bands with a band of fertilizer between and below the bands of seed. The bands are separated vertically and horizontally sufficiently to assist in reducing fertilizer damage to the seedlings, but close enough to allow the fertilizer, and particularly phosphate fertilizers, to be readily available to the seedling plants.
Typical arrangements for these side banding seeders include furrow opener assemblies with a single furrow opening member that has a separate port for receiving each stream and is configured to deliver each stream to a separate location so that the streams are placed in the soil in separate but closely adjacent rows or bands. An example of this arrangement is disclosed in U.S. Pat. No. 6,952,998 to Summach et al. Other furrow opener assemblies have two separate furrow opening members mounted on separate legs extending down from an arm. One of the streams is directed to each furrow opening member, and the streams are again placed in separate but closely adjacent bands. An example of this arrangement is disclosed in U.S. Pat. No. 5,396,851 to Beaujot.
Mid-row banding seeders provide the second route for dispensing seed and fertilizer in substantially separated locations. These seeders comprise two sets of furrow opener assemblies attached to the frame, one set to deposit a stream of fertilizer and the other to deposit a stream containing the seed and generally some phosphate fertilizer. The phosphate fertilizer, which does not move readily through the soil, is thus positioned near the seed, while the more readily moving nitrogen and sulfur are located farther away to avoid damage to seedlings.
An example of this type of mid-row banding seeder is disclosed in U.S. Pat. No. 6,216,616 to Bourgault. The Bourgault system uses one set of furrow opener assemblies to deposit the seed stream in laterally spaced seed furrows. The second set of furrow opener assemblies deposits the fertilizer stream in separate fertilizer furrows. Each fertilizer furrow is located about mid way between adjacent seed furrows, such that seed in each seed furrow draws nutrients from the fertilizer between them. While an equal number of fertilizer assemblies and seed assemblies can be provided it has been found to be effective to reduce equipment costs by providing only half as many fertilizer furrows as seed furrows, with the furrows arranged such that there are two seed furrows (SF) between successive fertilizer furrows (FF). Thus moving across the path of the air seeder the arrangement of furrows would be SF-FF-SF-SF-FF-SF-SF-FF-SF. Thus seed in each seed furrow draws the mid row banded nutrients from one direction only. The spacing between seed furrows in such machines is typically 10 to 12 inches, so the seed and fertilizer separation distance is about 5 to 6 inches.